End mills for metal cutting machinery have conventionally been produced as a single unit, comprising a fluted cutting portion and a cylindrical or conical shank portion sized to fit a machine spindle. However the increasing global pricing of modern tool alloys along with recently developed intricate surface treatment make it less economical, as the expensive shank material is wasted. It is therefore becoming common practice to produce a separate cutter (insert) made of high quality alloy or sintered carbide, which is then concentrically attached to the end of a reusable steel shank.
It is highly desirable that the cutter be easily replaced, upon wear, while leaving the shank in the machine spindle, such that no further adjustments are required after cutter replacement. A major requirement related to such accurate milling applications is that each replacement cutter be centered with repeatable accuracy to the true spindle axis of rotation and axially positioned correctly.
Currently, the majority of interchangeable cutter-shank combinations use a plain straight or conical thread coupler directly joining the cutter to the shank. Those tools require at least three turns of the cutter to completely withdraw the cutter from the shank. In an effort to reduce labor and machine downtime, it is desirable that the time interval required for cutter replacement be minimal.
It is known in the art of replaceable cutting tools, to reduce cutter interchange time by the aid of a quick release bayonet type rotative coupler, typically attaching a rear end section of a cutter to a front end section of a bolt, wherein both the bolt and the cutter are inserted together into a mounting hole having an appropriate centering surface for the cutter and a female thread provided in a shank. As a result of the male thread of the bolt engaging the female thread of the mounting hole, the cutter is drawn by the bolt and through the quick release rotative coupler towards the rear end side in the axial direction of the shank. The assembly is secured by tightening the cutter at the end of the thread stroke with a spanner. Upon applying the spanner in the opposite direction, the thread is initially slackened and the bayonet type rotative coupler is released, enabling quick change of the cutter with no need to slacken the entire length of the thread.
International class B23B 31/113 relates to quick release devices for spindle type cutting tools having bayonet couplers. Representative prior art is disclosed in U.S. Pat. Nos. 2,219,907 2,379,984 4,478,541 4,784,543 7,101,127 and U.S. Publication No. 2006/0127194.
U.S. Pat. No. 7,101,127 describes a cutter with a rear conical centering portion coaxially coupled to a two or three arm hook portion or anchor. The anchor is rotatively retained by bayonet action within a coupler in the form of a socket having a threaded rear portion for threadably engaging a tool shank. The socket, as shown in detail in FIG. 23A, has a shaped bore accessible from a front end of the socket for accommodating the bayonet and is undercut on opposing internal surfaces so as to form opposing recesses that retain mating surfaces of the anchor aims when the cutter is inserted and twisted. The assembly further includes stopper means limiting the relative rotation between the cutter and the socket to ensure correct positioning of the anchor arms. A similar arrangement is taught by US 2006/0127194 as shown in detail in FIGS. 2 and 6 thereof.
The need to provide such an undercut complicates the manufacturing process of the coupler, such action being particularly awkward when the coupler is closed around its periphery since access from the front end is restricted.
It would therefore be desirable to provide an improved bayonet type coupler for a quick release rotary cutting tool, where the need to provide undercuts in the socket is avoided.